Estradiol Secretion by Theca Cells of the Domestic Hen During the Ovulatory Cycle 1 , 2

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Abstract
In the domestic hen, estradiol-17.beta. (E2) secretion by preovulatory follicles decreases during follicular maturation. Experiments were performed to characterize this decrease in E2 production. Single Comb White Leghorn hens with regular laying sequences were used. The time of ovulation was determined by checking oviposition. At specific times during the ovulatory cycle, hens were killed and the F2 (2nd largest) and F3 (3rd largest) follicles were removed. Isolated theca cells were incubated in Medium 199 containing 0.1% gelatin and the medium assayed for E2. The optimum conditions for short-term incubation of theca cells were identified. The conditions tested were cell number, time of incubation, preferred androgen substrate, substrate concentration, and various concentrations of bovine serum albumin (BSA) and gelatin. The optimum conditions used were 1 .times. 106 cells/ml, 3 h incubation, 1 .times. 10-6 M testosterone (T) as substrate, and the addition of 0.1% gelatin to Medium 199. E2 secretion by F2 and F3 theca cells in the presence and absence (basal) of testosterone was measured. The F2 and F3 follicles were removed at 24, 18, 12, 6 and 2 h before ovulation and isolated theca cells incubated according to the conditions identified above. Basal E2 secretion by F3 theca cells was similar at 24, 18 and 12 h before ovulation but elevated (P < 0.05) at 6 h followed by a decrease (P < 0.05) at 2 h before ovulation. In the presence of T, E2 production was highest at 24 h, after which time there was a gradual decrease (P < 0.001) as the F3 follicle matured, with the exception of 6 h when production was greater than at 12 h (P < 0.001). Basal E2 secretion by F2 theca cells did not differ during the ovulatory cycle. E2 production, in the presence of T, was highest at 24 h and lower but with similar levels at 18, 12 and 2 h. Again, there was a significant increase in the conversion of T to E2 6 h before ovulation. While the profiles of E2 production by the F3 and F2 theca cells were similar, F2 theca cells converted approximately 50% less T to E2 than do F3 theca cells. The precise cause(s) for this significant in E2 secretion remains to be elucidated.